Biocides are chemical compositions that are widely used in industry for disinfection and to prevent microbiological contamination and deterioration of commercial products, materials and systems. Of the biocides presently available, phenolic biocides are widely used.
In general, phenolic biocides are colorless and have minimal toxicological effects to humans i.e., cause little or no irritation to the skin. Although most phenolics have a characteristic odor, some of them, such as phenylphenols and dichlorophenes, have little odor and others, such as triclosan, have none. These properties are desirable as they enable such biocides to be used as an ingredient in orally administered pharmaceutical preparations; as an approved biocide for use in food establishments and plants; and in packaging material.
Phenolic biocides also have other desirable properties including a wide biocidal spectrum against microorganisms, such as bacteria and fungi; residual bacteriostatic properties; and, unlike other biocides, are not readily deactivated by organic matter, such as blood, serum and milk. These biocides therefore have a wide application as disinfectants and antimold products in general household, industrial, and other areas requiring disinfection, as they can be used in the destruction of the microorganisms present or the prevention of their further proliferation to numbers that would be significantly destructive to the substrate or system being protected.
An example of a phenolic biocide is dichlorophene which, in addition to its antibacterial properties, is particularly effective against fungi, such as yeast mold and mildew. This property enables such derivatives to be used mainly as a preservative against mildew and rot in a variety of products including paper and textiles.
Another example of a phenolic biocide used is trichloro hydroxy diphenyl ether (Triclosan) which is an effective ingredient in deodorant and in skin cleansing preparations.
Hitherto, phenols have been used in industrial cleaners in an aqueous solution at very high pH (above pH 11). The use of cleaners with such high pH is undesirable in households. In order to overcome this problem, phenols have been used in alcoholic solution but such use leaves visable surface residues and is disadvantageous for household use.
To obtain aqueous detergent solutions of phenolic biocides they have first to be converted into their water soluble alkali salts, usually with sodium hydroxide, resulting in alkaline solutions of a pH of at least 11.0. The high alkalinity of these solutions excludes them from application in households and on surfaces susceptible to deterioration by alkalis. Their use has therefore been restricted to industrial cleaners for stainless steel equipment and hard floor surfaces in food processing and glass bottle washing plants and other industrial plants and areas where the higher alkalinity is acceptable.
When dissolved in an alcoholic-aqueous mixture with the addition of a small amount of a suitable surfactant to form a disinfectant cleaning preparation, such a solution will on drying leave streaks and partly greyish areas on treated surfaces due to the remaining insoluble residues of the biocide.
Triclosan which finds its main application in antiseptic skin and hand cleansing preparations has been either used in suspension, or solubilized with non-ionic surfactants with resultant loss in activity.
In mildew and rot proofing of paper and textiles phenylphenol and especially dichlorophene are widely used as their sodium salt solution for the impregnation of these materials against fungal infection and prevention of mold formulations.
The high alkalinity of these solutions causes weakening of the strength of fibers and loss of the biocides either by leaching out in moist climates or by lack of binding to the surfaces treated. This has been prevented in the past by neutralization of the alkali salt and/or bonding the biocides by means of a metal salt, such as zirconium acetate. These processes necessitate a further manufacturing procedure, use of additional equipment and additional cost for the neutralization agent. These additional measures are required as bonding the biocidal agent onto the material to be protected was not always effective, especially when prolonged periods of protection were required.